1885."] On the Formation of Vortex Rings by Drops. 431 



water, or by vibrations communicated to the capillary tube. If the 

 experiment be made with all care to avoid vibration, the stream falls 

 unbroken through a column of 8 inches of water : whilst if a tap 

 be given to the acid tube a break occurs in the stream, in consequence 

 of a momentary stop in the flow of acid, a small bead is formed, and 

 from it a ring. If no care is taken to avoid vibration the beads will 

 follow one another very rapidly. It may be objected that if there 

 existed a surface tension, it would only be when disturbances were 

 communicated that headings would appear. But in such a case, the 

 resolution into drops would be complete, and small spherules would 

 be formed between the larger drops. In fact, however, the con- 

 nexions between the headings are fine filaments of acid, so that the 

 headings are never really separated from one another. We have, 

 moreover, convinced ourselves of the correctness of this explanation, 

 by allowing a stream of cold water with lycopodium powder to flow 

 from a fine tube into a column of slightly warm water ; similar cessa- 

 tions in flow and formations of headings may be observed ; the rings 

 are not well formed, but this is to be expected, for the conditions are 

 not nearly so favourable. 



Experiments with two Liquids between ivhich there is Tension. 



When there is a very small tension between the liquid of the drop 

 and that in the column, some very interesting results are obtained . 

 In a few cases a ring is formed for a moment, but is almost imme- 

 diately broken up into drops and spherules. As instances of such 

 cases we may mention strong caustic potash solution dropped into 

 paraffin oil : strong sulphuric dropped into turpentine or into paraffin 

 oil : a certain mixture of turpentine and alcohol dropped into paraffin 

 oil : a mixture of alcohol and chloroform dropped into water : and 

 the mixture of alcohol and a few drops of water dropped into benzene 

 (see above, p. 423). In most cases the drop falls through the liquid 

 shaped like a disk, and in the first part of its course changes its shape 

 very considerably. These changes may be well observed in the case 

 of a drop of sodium sulphate solution falling through paraffin oil; 

 they are shown in fig. 10. 



At first the drop is nearly spherical (a) ; then it becomes flattened 

 (/3) ; next it becomes quite flat underneath or sometimes even hollow 

 (7), the top remaining curved. During all this time the velocity of 

 the drop has been changing. The top now gets flatter and flatter 

 (A 6 j £0> while it begins to bulge out at the bottom till the drop is 

 saucer-shaped (77, 0), hollow at the top, and rounded at the bottom, and 

 we perceive that it is followed close on by a vortex ring in the liquid of 

 the column. It now moves with constant velocity through the liquid 

 as though it met with no resistance, differing in this respect from the 

 case where the drop falls as a ring, when its velocity — unless th 



